code: def test_HandleMissingReturnNan(self):
      train = pd.DataFrame({"x": ["A", np.nan, "B"]})
      encoder = encoders.OneHotEncoder(
          handle_missing="return_nan", use_cat_names=True
      )
      result = encoder.fit_transform(train)
      pd.testing.assert_frame_equal(
          result,
          pd.DataFrame({"x_A": [1, np.nan, 0], "x_B": [0, np.nan, 1]}),
      )
  
imports: import pandas
  from unittest import TestCase
  import numpy
  import tests.helpers
  import category_encoders
label_desc: Use image node_id 11 for calling the TestOneHotEncoderTestCase obj's underlying member method code with example usage: obj.test_HandleMissingReturnNan() without return types